This invention relates generally to cryoanalgesia and more particularly to devices and procedures for applying cryoanalgesia to the neuroaxis.
Management of acute and chronic pain has been a concern for as long as medicine has been practiced. Many methods of inducing analgesia and anesthesia have been developed. The use of chemical substances is perhaps the most common approach to pain relief. This approach requires suitable substances that are effective, safe to humans, and do not cause complications or abnormal reactions. Despite the great advances that have been made in the field of anesthesiology, and in the field of pain relief in general, there are still some drawbacks to chemical-based approaches. For instance, the anesthetics generally available today must be administered in carefully graduated doses to assure the patient's well being, require extended periods of fasting prior to treatment, and are often accompanied by undesirable after effects such as nausea.
An alternate approach that avoids these drawbacks is cryoanalgesia, which is a safe and effective approach to providing prolonged pain relief without the complications or undesirable after effects often experienced with chemical-based approaches. As used herein, the term “cryoanalgesia” refers to cooling or freezing of neuronal tissue (nerves, synapses, ganglia, etc.) to produce analgesia or anesthesia. Attempts to use tissue cooling or freezing to control pain have been known since antiquity. Surgery using cold packs and the painless amputation of frozen limbs during wartime are part of military medical history. In the nineteenth century, attempts were made to use tissue cooling to treat a wide range of maladies. Twentieth century studies have shown that the cooling or freezing of neuronal tissue reduces or eliminates pain by interrupting nerve conduction. Cooling neuronal tissue to temperatures in the range of zero to −4 degrees centigrade, and sometimes below, causes analgesia lasting from days to weeks. Neuronal tissues cease functioning when sufficiently cooled, but before becoming frozen. Freezing neuronal tissue (i.e., reducing tissue temperature to −4 to −20 degrees centigrade or below) causes profound long lasting, usually permanent but sometimes reversible, anesthesia of the innervated part. There may well be different outcomes of cooling and freezing, depending on whether the treatment is applied to neuronal axons or neuronal cell bodies (containing the nucleus).
A number of devices for the controlled cooling and/or freezing of small volumes of tissue are available. Rigid cryoprobes exist for percutaneous use or in open invasive surgical procedures. For example, cryoprobes are used for freezing a range of lesions from prostate tissue to metastatic cancers in liver. Neuronal tissue has been frozen with such devices for the relief of pain. Such devices have been in use for more than 20 years.
Cryocatheters or cryogenic catheters are of more recent evolution and have been used by way of the blood vascular route to destroy, by freezing, conducting tissues in the heart for the correction of cardiac arrhythmia. Such cyrocatheters are not designed for cryoanalgesia.
In both these types of systems, coolant gases under pressure are delivered to the tip of the instrument (i.e., the probe or catheter) where expansion of the gas is used to create temperatures as low as −60 degrees centigrade or below which cools or freezes the tissues in the local area around the tip. The size and configuration of the lesion created will depend in large part on a configuration of the tip. The effect obtained will depend upon the rate of cooling, degree of cooling, and the duration of cooling, as well as specifics of the tissue and environment.
While conventional cryoprobes used to treat neuronal tissue can produce excellent results, they generally can be used only for certain percutaneous procedures in which the target neuronal tissue is readily accessible by the rigid probes or for open surgical procedures. These restrictions greatly limit the opportunities for using cryoanalgesia. Accordingly, it would be desirable to have a device and method that would allow a more extensive use of cryoanalgesia.